[keycloak-dev] Moving modules to modules/system/layers/keycloak and modules/system/add-ons/keycloak

Currently all our modules are in module/system/layers/base. This is not good from a patching perspective. Modules for the standalone server should be in modules/system/layers/keycloak. Modules for adapters and server overlay should be in modules/system/add-ons/keycloak. I've asked Marko to sort this out so that it's fixed for 1.9.0.